$28+2x=55-(-13)$
$↔28+2x=68$
$↔2x=68-28$
$↔2x=40$
$↔x=20$
Vậy $x=20$
$----------$
$|x+5|+(-10)=-5$
$↔|x+5|-10=-5$
$↔|x+5|=5$
$↔\left[\begin{array}{l}x+5=-5\\x+5=5\end{array}\right.↔\left[\begin{array}{l}x=-10\\x=0\end{array}\right.$
$----------$
`6n-11\vdots n-2`
`->6n-12+1\vdots n-2`
`->6(n-2)+1\vdots n-2`
`->1\vdots n-2`
`->n-2 \in Ư(1)`
`->n-2 in {-1;1}`
`->n in {1;3}`